During voice and data transmission, signaling messages are also conveyed over the air interface in addition to user data. Signaling messages allow the network and the mobile station to discuss the management of importance issues, such as resources and handovers. When traffic is ongoing, signaling messages are carried through the Associated Control Channels (ACCH). The Slow Associated Control Channel (SACCH) is used for non-urgent procedures—mainly for the transmission of radio measurement data needed for handover decisions on a dedicated physical subchannel. The SACCH has the particularity that continuous transmission must occur in both directions. The SACCH is actually always present on dedicated physical subchannels (3GPP TS 43.051 v5.1.0 Release 5). As specified in “Digital Cellular Telecommunications System (Phase 2+), Mobile Radio Interface Layer 3 Specification, Radio Resource Control Protocol” (GSM 04.18 v8.8.0 Release 1999), each SACCH block conveys: 1) one physical layer header of two octets (the physical layer implements a peer-to-peer protocol for the control of timing advance and power control at the operation on dedicated physical sub-channels, and 2) one Layer 2 frame of 21 octets. Thus, each SACCH block contains 184 information bits. When a 40-bit FIRE code and a 4-bit tail section are added to the information bits, the block code contains 228 bits. After the block code is encoded with a ½ convolutional code (of which the constraint length is 5) and interleaved, the coded SACCH block contains 456 bits reordered and partitioned into 4 blocks, each of which contains 114 bits of interleaved data. Each block is then mapped onto one burst of which the stealing flags are set to “1” (GSM TS 05.03 v8.6.1 Release 1999).
It has been proposed that a fixed amount of bits out of every SACCH burst is punctured in order to convey some signaling messages at a rate of once every 120 ms. However, such puncturing decreases the link level performance of the SACCH.
It is advantageous and desirable to provide a method of inband signaling using the SACCH without decreasing the link level performance of the SACCH.